Perpendicular magnetic recording has been developed in part to achieve higher recording density than is realized with longitudinal recording devices. A PMR write head typically has a main pole layer with a small surface area at an ABS, and coils that conduct a current and generate a magnetic flux in the main pole such that the magnetic flux exits through a write pole tip and enters a magnetic medium (disk) adjacent to the ABS. Magnetic flux is used to write a selected number of bits in the magnetic medium and typically returns to the main pole through two pathways including a trailing loop and a leading loop in a shield structure. The trailing loop comprises a trailing shield structure with first and second trailing shield sides at the ABS. The second (PP3) trailing shield arches over the write coils and connects to a top surface of the main pole above a back gap magnetic connection. The first trailing shield has a high moment (>19 kG to 24 kG) layer called a hot seed layer that adjoins a top surface of the write gap. A good hot seed response is required to reduce stray fields in the side shields and leading shield, and provide a better down-track field gradient. The leading loop includes a leading shield with a side at the ABS and that is connected to a return path proximate to the ABS. The return path extends to the back gap connection and enables magnetic flux in the leading loop pathway to return from the leading shield at the ABS and through the back gap connection to the main pole. A PMR head which combines the features of a single pole writer and a double layered medium (magnetic disk) has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density.
For both conventional (CMR) and shingle (SMR) magnetic recording, continuous improvement in storage area density is required for a PMR writer. A write head that can deliver or pack higher bits per inch (BPI) and higher tracks per inch (TPI) is essential to the area density improvement. A fully wrapped around shield design for a PMR write head is desired where the trailing shield is responsible for improving down track field gradient while side shields and a leading shield improve the cross track field gradient and TPI as well as adjacent track erasure (ATE) performance. To avoid wide adjacent track erasure (WATE), all shields preferably are made of a <19 kG material. A double write shield (DWS) design may be employed wherein the main pole and hot seed in the first trailing shield are comprised of high moment (>19 kG to 24 kG) material while the leading shield and side shields are made of low moment 10-16 kG material, and the trailing shield structure is made of 16-19 kG material. If writeability can be sustained, a thinner write gap at the main pole trailing (top) surface and a narrower side gap adjoining the main pole sides in the cross-track direction are preferred for better track field gradient (Hy_grad, BPI) and cross-track field gradient (Hy_grad_x, TPI), respectively. To enhance writeability, side shield height reduction is important not only to reduce main pole flux shunting to the side shields, but also to allow more main pole volume closer to the ABS. However, side shield saturation may degrade Hy_grad_x and TPI capability, and is a concern with advanced side shield structures with a height of about 0.3 microns or less.
The key to an optimized PMR writer structure is the capability to control distribution of magnetic flux from the main pole to each shield. Ideally, better control of magnetic flux in the near field or proximate to the main pole is desirable to achieve an enhanced near field gradient and to realize higher ADC. Typically, flux distribution is controlled by changing the magnetic saturation (Ms) of materials in the shields, and by modifying geometries (size and shape) of the shields. However, additional methods of tuning magnetic flux distribution are needed to provide better control and flexibility to enable PMR writers with higher TPI capability to at least 400K/in for CMR and at least 500K/in for SMR.